1. G. Valtchev, M. Neshkova, A. Nikolov Nuclear Power Plant Kozloduy
MODERNIZATION OF THE ACCIDENT LOCALIZATION SYSTEM AND RELEVANT DOSE EXPOSURE ON UNIT 4 OF KNPP
G. Valtchev, M. Neshkova, A. Nikolov
Nuclear Power Plant Kozloduy
NPP Kozloduy, 3321 Kozloduy, Bulgaria
Phone:
Kozloduy NPP, Radiation protection department

2. Modernization of ALS
Due to modernization activities in 2001 the outage of unit 4 was prolonged to 4 months, ( ). The projected collective dose was 1610man.mSv.
Modernization of Accident Localization System (ALS) was foreseen. The projected collective dose (dose budget) for ALS activities only was 300man.mSv.
This dose budget was based on the technology used and the expected working time for the main activities. Consideration was given to the gamma dose rate too.
Kozloduy NPP, Radiation protection department

3. Modernization of ALS
The gamma dose rate on the working places in the Restricted Control Area (RCA) was mSv/h.
For a short-time activities, on some hot spots the dose rate was 0.80 mSv/h.
The project was performed by subcontractor. The modernization activities started from the first days along to the end of the outage.
Kozloduy NPP, Radiation protection department

4. Modernization of ALS The existing ALARA approach was implemented:
Instruction of the personnel about used technology and systems location;
Gamma dose rate mapping at the entrance of the RCA;
Pre-briefing of workers;
All preparatory work was performed outside the RCA;
Decontamination of the floor;
Individual dose control by TLD and alarm electronic dosimeters;
Weekly management meetings.
Kozloduy NPP, Radiation protection department

5. Modernization of ALS
To the end of ALS modernization about 606 Radiation Work Permits were issued.
No one worker received a dose higher then 0.25mSv/day.
The real collective dose for all ALS activities was 243.4man.mSv, and for the whole outage man.mSv.
About 35 different tasks were observed.
Kozloduy NPP, Radiation protection department

6. Modernization of ALS
Dosimetry with TLD badges and electronic alarm dosemeters were used for the dose control of the personnel;
The highest permissible dose in the Radiation Work Permit was 0.5 mSv;
The maximum permissible accumulated individual dose for all ALS modernization 5 mSv;
A daily analysis and comparison of the expected and committed dose;
Dose rate mapping was performed in any single RWP;
Continuous monitoring of the levels of air contamination.
Kozloduy NPP, Radiation protection department

7. Modernization of ALS Dose distribution analyzes were performed.
The RWP were grouped in 6 main tasks:
Dismantling of valves –123 RWP with 47 man.mSv;
Mounting of valves –31 RWP with 20.1 man.mSv;
Metal control –11 RWP with < 1man.mSv;
Preparation activities for mounting –67 RWP with 37.8 man.mSv;
Sawing, drilling and transportation -254 RWP with 90.2 man.mSv;
Mounting activities of ALS (all) –96 RWP with 42 man.mSv;
Kozloduy NPP, Radiation protection department

8. Modernization of ALS
The dose distribution is shown on the following chart:
Kozloduy NPP, Radiation protection department

9. Modernization of ALS
A programme for minimization of radioactive waste generation was implemented:
Over 210 m3 mixed waste was generated;
Only 5 m3 was determined as low as radioactive waste.
Kozloduy NPP, Radiation protection department

10. Modernization of ALS Conclusion:
Good work management and first attempt of effective empowerment of the workers gave satisfactory results
Although the work was performed for a first time the ALARA implementation reduced the projected collective dose by 19 %
Kozloduy NPP, Radiation protection department